1. Field of the Invention
The present invention relates to a seat suspension device provided in an automotive seat, and in particular to an arrangement in the seat suspension wherein a hydraulic damper is disposed.
2.Description of Prior Art
Conventionally, a seat suspension device used in an automotive seat is of such a basic construction that a pair of X-shaped links are interposed between an upper frame on which a seat cushion is mounted and a lower frame fixed to a floor of the automobile, with a hydraulic damper being disposed therein. Typically, the hydraulic damper is disposed aslant between the upper and lower frames with a view to making greater the vertical movable range of the upper frame with respect to the lower frame. In other words, such arrangement is intended for eliminating any limit against the vertical movable range of the upper frame relative to the lower frame.
However, in most instances, this kind of hydraulic damper is generally disposed at a center point beween the two X-shaped links, acting as a means for buffering an impact applied to the upper and lower frames. This construction has been found defective in that the hydraulic damper is just situated beneath the seat cushion, thus posing the likelihood that, when a heavy occupant sits on the seat, the seat cushion will be lowered to contact with the hydraulic damper, leaving an unpleasant feeling. Further, by the reason of the damper being disposed aslant, a repercussive force given from the damper is oriented aslant in relation to the vertical direction of a load applied to the upper frame, with the result that no full repercussive force is exerted from the damper against the load and thus the upper frame is lowered so quickly that the occupant may not feel any comfortable bottoming touch of the seat. In this aspect, the seat suspension device having the hydraulic damper disposed vertically between the upper and lower frames is superior to that one in terms of achieving a proper repercussive force or slow, comfortable bottoming touch of the seat, since the repercussive force of the damper corresponds in direction to a load applied to the upper frame. Yet, this vertical type of damper has also been found defective in that the distance between the upper and lower frames must be widened more in order to install the damper in an upright state between the two frames, which results in increasing the height of the seat to shorten the distance between the seat and the cabin ceiling.